Plate Boundaries
- Earthquakes and volcanoes occur in regions where the edges of different plates are in contact
- So, scientists have been able to identify tectonic plates by gathering and plotting data about:
- The epicentres of major earthquakes
- The sites of active volcanoes
World map of earthquakes and volcanoes
The position of earthquakes and volcanoes provides evidence for tectonic plates
Types of plate boundary
- Volcanic eruptions and earthquakes most commonly occur at or near plate boundaries
- There are main types of plate boundaries:
- Constructive
- Destructive
- Conservative
Constructive plate boundary
- At a constructive boundary, tectonic plates are moving apart
- The Mid-Atlantic Ridge is an example of a constructive plate boundary
- Both volcanic eruptions and earthquakes occur at this type of plate boundary
- The volcanic activity produces new igneous rock
Constructive Plate Boundary
Destructive plate boundary
- At a destructive plate boundary, the plates are moving together
- One tectonic plate is pushed down into the mantle where it melts to form magma
- The boundary between the Nazca plate and the South American plate is one example
- Both volcanic eruptions and earthquakes occur at this type of plate boundary
- Volcanoes at destructive plate boundaries are explosive
Destructive Plate Boundary
Conservative boundary
- At a conservative boundary, the plates move past each other in opposite directions or the same direction at different speeds
- The San Andreas fault is an example of a conservative plate boundary
- Powerful earthquakes are the only hazard at this type of boundary
- There are no volcanoes because melting does not occur
Conservative Plate Boundary Diagram
At a conservative plate boundary, tectonic plates slide past each other
Examiner Tip
You are not expected to recall the detailed structures of these boundary types
